Bit rate control mechanism for digital image and video data compression

DETAILED DESCRIPTION What is claimed is: 1.
A bit rate controller for a moving image data compression encoder comprising: means in response to an actual bit rate for a prior coded block of the moving image data for generating a complexity factor as a function of a prior complexity factor and a prior quality factor for the prior coded block; and means for computing a quality factor for a present block of the moving image data compression decoder as a function of the complexity factor and a target bit rate for the present block.
2.
The bit rate controller as recited in claim 1 further comprising: means for projecting a virtual buffer occupancy as a function of the quality factor; and means for controlling a width of a processing window for the generating means so that the virtual buffer occupancy does not overflow or underflow.
3.
The bit rate controller as recited in claims I or 2 further comprising: means for estimating an activity factor between images of the moving image data; and means for indicating a scene change to initialize the generating means when the activity factor indicates an abrupt change between images.
4.
A method of bit rate control for digital image and video compression of the type wherein a quality factor for controlling a quantizer for a current block of samples of a video signal is generated by a rate controller as a function of a bit rate for a prior block of samples of the video signal comprising the steps of: estimating a complexity parameter for the current block of samples as a function of a prior block of samples including the bit rate; and determining from the complexity parameter the quality factor for output from the rate controller.
5.
The method as recited in claim 4 further comprising the steps off detecting a scene change in the video signal; and resetting the rate controller prior to the estimating step when the scene change is detected by the detecting step.
6.
The method as recited in claims 4 or 5 further comprising the steps of: projecting a virtual buffer occupancy as a function of a prior occupancy and an average bit rate; and controlling a processing window for the estimating step so that the virtual buffer occupancy does not overflow or underflow